The invention relates generally to a thin film device and more particularly, to a method of electrochemically depositing a thin film of material that is substantially insoluble in water. Electrochemical deposition is made possible by increasing the solubility of the substance which is either sparingly soluble or insoluble in water by providing a micelle solution of a surfactant and electrochemically depositing the substance on an electrode. Such thin films are advantageously included in color filters for display devices, optical disks, electrophotographic photoreceptors and nonlinear switching elements as well as a wide variety of other applications.
Organic pigments such as phthalocyanine have recently become of interest as functional materials. The characteristic structure of these organic pigments are useful for photoconductors or optical devices. Because these organic pigments are generally either only sparingly soluble or insoluble in water, liquid processes are rarely adopted for producing thin films. Attempts have been made at converting substantially insoluble organic pigments into solvent-soluble pigments and forming a thin film by emersion coating methods or the like. Unfortunately, this method only provides an extremely thin film which has seriously restricted application of this method.
Employing a Langmuir Blodgett technique has similar drawbacks. Fine particles of an organic pigment can be kneaded with an organic binder and thinly coated to form a functional film. However, this method is inadequate for fully utilizing the properties of the functional substance to be formed in the thin film due to the presence of the binder.
Thin films of these substantially insoluble substances are conventionally formed by deposition, sputtering or chemical vapor deposition (CVD), but these methods also have drawbacks. For example, when a thin film is formed by one of these methods, the chemical structure of the thin film produced differs from that of the raw material and reproduction of the initial crystalline structure is often impossible even if the same chemical structure is produced. Further, such vacuum processes are expensive and improperly suited to mass production.
Another technique for forming these films has been proposed by Saji and others (Chem. Lett., 1431, (1987), J. Am. Chem. Soc., 109, 5881 (1987), Chem. Lett., 893 (1988), Synopses of Lectures of 55th Meeting of the Electrochemical Society of Japan). This method forms a thin film by solubilizing a hydrophobic pigment or a polymer in an aqueous micelle of an oxidizable and reducible surfactant formed of a ferrocene derivative in an aqueous medium. The solubilized pigment or polymer is deposited on an electrode by electrolysis. However, surfactants and other substances heretofore reported as adaptable to this method are extremely limited.
Accordingly, it is desireable to provide an improved method for depositing thin films of substantially insoluble substances by electrolytic techniques.